Green synthesis and multifunctional applications of nitrogen-doped carbon quantum dots via one-step hydrothermal carbonization of Curcuma zedoaria

Low-dimensional (<10 nm) semiconductor carbon quantum dots (CQDs) have been widely used in metal ion sensing and bioimaging. Here, we used the renewable resource Curcuma zedoaria as a carbon source and prepared green carbon quantum dots with good water solubility by a hydrothermal method without any chemical reagent. At different pH values (4–6) and high NaCl concentrations, the photoluminescence of the CQDs was very stable, which indicated that they were suitable for a wide range of applications even under harsh conditions. The CQDs exhibited fluorescence quenching in the presence of Fe3+ ions, indicating their application potential as fluorescence probes for the sensitive and selective detection of Fe3+ ions. The CQDs showed high photostability, low cytotoxicity, and good hemolytic activity, and were successfully applied to bioimaging experiments, i.e. multicolor cell imaging in L-02 (human normal hepatocytes) and CHL (Chinese hamster lung) cells with and without Fe3+, as well as wash-free labeling imaging of Staphylococcus aureus and Escherichia coli. The CQDs also showed good free radical scavenging activity and demonstrated a protective effect against photooxidative damage to L-02 cells. These results indicate that CQDs obtained from medicinal herb sources have multiple potential applications in the fields of sensing, bioimaging, and even disease diagnosis.